This invention relates generally to fluid delivery systems and more particularly to valve assemblies that must handle particulate-containing fluids.
It is common to pump fluids that contain particulates into oil and gas wells. For example, fracturing fluids typically contain proppant particles, such as sand or small beads,(sizes typically from U.S. Standard Sieve sizes 10 through 60). Reciprocating plunger pumps are frequently used to create the high-pressure fluid flow needed to inject fluids, such as fracturing fluids, into oil and gas formations. These pumps typically include valve assemblies that are biased toward the closed position. When the motion of the plunger creates a differential pressure across the valve, the differential pressure forces the valve open, allowing the fluid to flow through the valve. However, solid particles in the fluid can become trapped within the valve assembly upon valve closure, creating damage to valve assembly components and reducing the useful life of the valve assembly.
The valve assembly will typically contain an area where two metal surfaces contact each other when the valve is closed. The solid particles from the fluid can become trapped between the two metal contact surfaces in specific locations rather than evenly distributed across those surfaces, creating concentrated stress forces at these locations. These concentrated stress forces can lead to localized pitting. Once pitting has occurred, the solid particles tend to concentrate at the location of the pitting, which in turn accelerates the damage at these locations.
Valves used for slurry service typically have a resilient sealing insert around the outer perimeter of the valve closure member to provide effective valve sealing. Pressure applied to a closed valve forces the resilient sealing insert to become a hydraulic seal, extruded into the gap between the valve closure member and the valve seat member. For the insert to effect a hydraulic seal upon valve closure, the insert must protrude from the valve closure member toward the valve seat member when the valve is open. When the valve is nearly closed, the resilient sealing insert contacts the valve seat member. When the valve is closed, the resilient sealing insert is deformed against the seat member to form the hydraulic seal, and metal-to-metal contact occurs between the valve closure member and the valve seat member. Proppant trapped under the resilient sealing insert can become temporarily or permanently embedded in the resilient insert material, so that the insert can effect a hydraulic seal in the presence of proppant. In the presence of proppant, the metal surfaces of the valve closure member and valve seat member do not form a hydraulic seal.
The resilient sealing insert of current valves is on the outer perimeter of the valve closure member or valve seat member, so that applied pressure will deform the resilient sealing insert to seal between the valve closure member and the valve seat member. If the resilient sealing insert were on the inner perimeter of the valve closure member or valve seat member, then applied pressure would force the resilient sealing insert away from the contact area between the valve closure member and the valve seat member, and the valve would not seal.
The resilient sealing insert of current valves contacts the valve seat member before the valve closure member contacts the valve seat member. The gap between the sealing insert and the seat of an open valve is smaller than the gap between the valve closure member and the valve seat. When the valve is closing, the gap between the sealing insert and the valve seat member becomes too small to pass particles in the fluid, while the gap between the valve closure member and the valve seat member is still large enough to pass particles into the region between them. Thus a standard valve sealing insert can act as a forward screening element that concentrates proppant particles in the region between the valve closure member and the valve seat member. Such concentrations of proppant particles cause damage to the contacting surfaces of the valve closure member and the valve seat member.
If the pump is operated in such a way as to have significant valve lag, i.e. a discharge valve does not close until well after the plunger starts its suction stroke, there will be reverse flow through the valve before it closes. The standard sealing insert will screen out proppant particles from the reverse fluid flow, preventing the particles from entering the region between the valve closure member and the valve seat member. However, the volume of fluid which flows through current valves during the short time interval between the onset of such reverse particle screening and the closure of the valve typically is insufficient to displace the proppant-laden fluid from the valve before closure. Particles are still trapped between the valve closure member and the valve seat member.
Conventional liquid end valve assemblies may also experience failures due to foreign objects becoming lodged within the valve assembly (e.g., bolts or gravel can accidentally enter the fluid flow path). These foreign objects can become wedged between the contact surfaces of the valve, and thus prevent the valve from closing.
There is a need for improved valve assemblies that reduce the incidence of damage caused by particulates or foreign objects in well treating fluids.
The present invention relates to valve assemblies that can reduce the problem of solid particle damage within the valve, and can also help reduce or avoid the problems associated with foreign objects becoming lodged within the valve. This invention is well suited for use with pumps that inject particle-laden fluid during the treatment of oil and gas wells, but could be used for other purposes as well.
One aspect of the invention is a valve apparatus that can screen particles from fluid flowing forward through the valve. This valve apparatus has a longitudinal axis therethrough and comprises a valve seat member, a valve closure member, a fluid flow path, and a forward screening member. The valve seat member is usually stationary, and comprises a hollow bore and a first frustoconical contact surface. The valve closure member comprises a body and a second frustoconical contact surface that is adapted to seal against the first frustoconical contact surface. The valve closure member is movable along the longitudinal axis of the valve apparatus (i.e., toward and away from the valve seat member). The fluid flow path extends through the bore of the valve seat member and between the valve seat member and the valve closure member. This fluid flow path is closed when the second frustoconical contact surface is sealed against the first frustoconical contact surface. The forward screening member is attached to at least one of the valve closure member or the valve seat member. This forward screening member screens particles from fluid passing through the fluid flow path in a forward direction when the valve closure member approaches the valve seat member. This results in preventing the screened particles from entering the region between the valve closure member and the valve seat member. To perform such forward flow screening, the forward screening member may be located around the inner perimeter of the region between the valve closure member and the valve seat member.
In one embodiment the forward screening member comprises a cylindrical plug that is near the inner perimeter of the second frustoconical contact surface and can extend into the bore of the valve seat member. The valve seat member comprises a cylindrical inner wall, and a screening gap exists between the cylindrical inner wall and the cylindrical plug when the valve closure member is near to the valve seat member. This screening gap is small enough to prevent passage of particles of a selected size from passing through the fluid flow path. The particles to be screened out will generally consist of proppant particles having a generalized average diameter of about 0.01-0.10 inches and a likely average diameter of 0.02-0.07 inches. The cylindrical plug can further comprise a first cylindrical section having a first diameter and a second cylindrical section having a second diameter that is greater than the first diameter. The screening gap between the second section and the cylindrical inner wall is small enough to prevent particles of a selected size from passing through the fluid flow path.
In another embodiment at least one of the valve closure member and the valve seat member comprises a resilient insert near the inner perimeter of a frustoconical contact surface. The resilient insert can be attached to the valve closure member and extend further toward the first frustoconical contact surface than the second frustoconical contact surface does.
In yet another embodiment the forward screening member comprises a screening insert that is near the inner perimeter of either the first or second frustoconical contact surface, and a screening gap exists between the forward screening insert and the opposing frustoconical contact surface when the valve closure member is near to the valve seat member. The screening gap is small enough to prevent particles of a selected size from passing through the valve assembly. The forward screening insert can be a resilient screening insert. The forward screening member can comprise a plurality of forward screening inserts near the inner perimeter of either the first or second or both frustoconical contact surfaces. The resilient forward screening insert can be attached to the valve seat member and contact the second frustoconical contact surface when the valve closure member approaches the valve seat member. The forward screening insert can also be attached to the valve closure member. The forward screening insert can extend into the bore of the valve seat member. When there are more than one forward screening inserts at least one of the forward screening inserts can extend into the bore of the valve seat member.
Another aspect of the invention is a valve apparatus that can screen particles from fluid flowing in reverse through the valve. This reverse flow occurs when there is valve lag, and the discharge valve does not close before the plunger starts its suction stroke. In contrast to the small amount of particle screening typically done by a standard resilient sealing insert on the outer perimeter of the valve assembly during the short time interval between the onset of reverse screening due to valve lag and the closure of the valve in current valves, the reverse screening apparatus of the present invention can prolong that time interval until a sufficient volume of filtered fluid flows into the region between the valve closure member and the valve seat member to displace proppant laden fluid from that region. Although there can be some reverse flow and reverse particle screening with current resilient sealing insert designs, the volume of filtered fluid can not be sufficient to displace the particle laden fluid from the region between the valve closure member contact surface and the valve seat member contact surface.
One aspect of the present invention positions the valve through mechanical means such as a cam or hydraulic positioner. The optimal valve positioning for pumping particle-laden fluids includes valve lag and reverse screening. The positioning mechanism delays the valve closure member""s descent temporarily within a range of reverse screening heights above the valve seat such that the resilient sealing insert screens out proppant particles from the fluid in reverse flow into the valve, and the frustoconical contact surfaces are held far enough apart for proppant-laden fluid to pass between them. The proppant particles are concentrated outside the valve where they cannot interfere with valve closure or damage the valve contact surfaces. Then after sufficient reverse fluid flow occurs to displace the proppant-laden slurry from the region between the valve closure member and the valve seat member with fluid from which the proppant had been screened, the valve closure member is lowered fully to close the valve. The valve closure member and the valve seat member contact each other with no proppant particles in between them to be crushed and damage the contacting surfaces of the valve closure member and the valve seat member.
As an alternative to mechanical valve positioning, another aspect of the present invention is a valve apparatus which uses the resilient sealing insert as a spring to effect the delay of the valve closure member descent within a range of screening heights above the valve seat member and allow reverse screening to clear proppant-laden fluid from the region between the valve closure member and the valve seat member. This apparatus has a longitudinal axis therethrough and comprises a valve seat member, a valve closure member, a fluid flow path, and a reverse screening member. The valve seat member is usually stationary, and comprises a hollow bore and a first frustoconical contact surface. The valve closure member comprises a body and a second frustoconical contact surface that is adapted to seal against the first frustoconical contact surface. The valve closure member is movable along the longitudinal axis of the valve apparatus (i.e., toward and away from the valve seat member). The fluid flow path extends through the bore of the valve seat member and between the valve seat member and the valve closure member. This fluid flow path is closed when the second frustoconical contact surface is in contact with the first frustoconical contact surface. The reverse screening member is attached to at least one of the valve closure member or the valve seat member. This reverse screening member screens particles from fluid passing through the fluid flow path in a reverse direction when the valve closure member approaches the valve seat member. The fluid without the particles flows into the region between the valve closure member and the valve seat member, and displaces particle-laden fluid from that region before the valve closes.
In one embodiment of the invention at least one of the valve closure member and the valve seat member comprises a resilient insert near the outer perimeter of a frustoconical contact surface. The resilient insert can be attached to the valve closure member and extend further toward the first frustoconical contact surface than the second frustoconical contact surface does. A valve exit gap exists between the resilient insert and the first frustoconical contact surface that varies in size as the valve closure member moves relative to the valve seat member. When reverse flow occurs through the valve, this valve exit gap becomes the entrance for the reverse flowing fluid entering the valve assembly.
The reverse screening member can comprise a screening insert that is near the outer perimeter of either the first or second frustoconical contact surface. A screening gap can exist between the reverse screening insert and the opposing frustoconical contact surface when the valve closure member approaches the valve seat member. The screening gap can be small enough to prevent particles of a selected size from passing through the valve assembly, while the gap between the frustoconical contact surfaces is still large enough to allow passage of particle-laden fluid. The reverse screening member can be a resilient screening insert. The reverse screening member can comprise a plurality of screening inserts near the outer perimeter of either the first or second or both frustoconical contact surfaces. The reverse screening member can be attached to the valve seat member and contact the second frustoconical contact surface when the valve closure member approaches the valve seat member. The reverse screening member can also be attached to the valve closure member and contact the first frustoconical contact surface when the valve closure member approaches the valve seat member.
The valve closure member has an outer perimeter and the resilient insert can be located at said outer perimeter. This will create a valve exit gap between the resilient insert and the first frustoconical contact surface, the size of the valve exit gap varying with the radial distance from the outer perimeter.
A screening gap can exist between the resilient screening insert and the first frustoconical contact surface when the valve closure member approaches the valve seat member. The screening gap can be small enough to prevent particles of a selected size from passing through the screening gap, while the gap between the frustoconical contact surfaces is still large enough to allow particle-laden fluid to pass between them. Proppant particles can be trapped between the reverse screening member and the first frustoconical contact surface. These particles can hold the valve closure member up above the valve seat member, until sufficient differential pressure exists to deform the resilient screening insert and effect a hydraulic seal. When the plunger moves to create reverse flow through a valve, a differential pressure is created across the valve. Fluid from which the proppant particles have been screened can pass into the valve, and can displace proppant-laden fluid from the region between the frustoconical surfaces. The proppant particles trapped between the reverse screening insert and the valve seat member can hold the valve open to provide a gap between the valve closure member contact surface and the valve seat member contact surface sufficiently wide to allow the proppant laden fluid in the gap to move, carrying the proppant particles out of the valve. When the plunger velocity increases, the flow velocity across the valve and the differential pressure across the valve increase. Downward force on the valve closure member due to the differential pressure can deform the resilient reverse screening insert and close the valve.
In another embodiment of the present invention, the resilient reverse screening insert can comprise at least one protrusion on its surface that contacts the valve seat member when the valve closure member approaches the valve seat member. The resilient insert can further comprise a non-resilient element having at least one protrusion on its surface that contacts the valve seat member when the valve closure member approaches the valve seat member. The protrusions can temporarily delay the downward motion of the valve closure member within a range of screening heights above the valve seat member where the screening gap between the reverse screening insert and the valve seat member is small enough to prohibit passage of particles of a selected size and where the gap between the frustoconical contact surfaces is still large enough to allow passage of particle-laden fluid. The screening gap can be maintained until sufficient differential pressure exists to deform the insert protrusions and close the valve. The screening gap can also be created by at least one protrusion from the first frustoconical contact surface in the area contacted by the resilient insert. The screening gap can be created by at least one protrusion on each of the resilient insert and the first frustoconical contact surface.
The protrusions can have the form of small bumps. The shape of the protrusions is not important. The protrusions simply hold the resilient insert up enough to allow fluid without particles to pass between the insert and the opposing frustoconical surface. The protrusions can have many other forms such as a series of small ridges, a knurled pattern or a wavy surface. A combination of protrusions on the insert and on the opposing frustoconical contact surface can also be provided.
The valve closure member can further comprise a bypass fluid flow path between the resilient insert and the body of the valve closure member. The bypass fluid flow path can have a size small enough to prevent particles of a selected size from passing therethrough, while the gap between the frustoconical contact surfaces is still large enough to allow passage of particle-laden fluid. The bypass fluid flow path can be created by at least one protrusion on the valve closure member body that spaces the resilient insert away from the rest of the valve closure member. The bypass fluid flow path can also be created by at least one protrusion on the resilient insert that spaces the valve closure member body away from the rest of the resilient insert. The bypass fluid flow path can be created by at least one protrusion on each of the resilient insert and the valve closure member body. The bypass flow path can be maintained until sufficient differential pressure exists to deform the insert and close the path.
An additional aspect of the present invention is a valve apparatus that can screen foreign objects (such as bolts or rocks) from the fluid passing into the valve assembly. By screening the foreign objects from the fluid, they are prevented from becoming lodged between the contact surfaces and preventing the valve from closing. This can result in fewer unplanned shutdowns for valve maintenance and can improve valve efficiency.
This embodiment comprises a valve apparatus that has a longitudinal axis therethrough and comprises a valve seat member, a valve closure member, a fluid flow path, and a screening member. The valve seat member is usually stationary, and comprises a hollow bore and a first frustoconical contact surface. The valve closure member comprises a body and a second frustoconical contact surface that is adapted to seal against the first frustoconical contact surface. The valve closure member is movable along the longitudinal axis of the valve apparatus (i.e., toward and away from the valve seat member). The fluid flow path extends through the bore of the valve seat member and between the valve seat member and the valve closure member. This fluid flow path is closed when the second frustoconical contact surface is sealed against the first frustoconical contact surface. The screening member is attached to at least one of the valve closure member or the valve seat member. This screening member screens foreign objects from fluid passing through the fluid flow path in a forward direction when the valve closure member approaches the valve seat member.
In one embodiment the screening member can comprise a cylindrical plug that is near the inner perimeter of the second frustoconical contact surface and that extends into the bore of the valve seat member. In this embodiment of the invention the valve seat member comprises a cylindrical inner wall, and a plug gap exists between the cylindrical inner wall and the cylindrical plug. This plug gap is small enough to prevent passage of foreign objects, such as bolts or gravel. A valve exit gap will exist between the resilient sealing insert and the first frustoconical contact surface that varies in size as the valve closure member moves relative to the valve seat member, and it is preferred that the maximum size of the valve exit gap is at least as large as the plug gap. This will allow any material that enters through the plug gap to exit through the valve exit gap. The maximum size of the valve exit gap will depend on the amount of valve lift. Valve lift can be increased if the fluid forces on the screening member are greater than the fluid forces normally applied to a valve closure member without the screening member.
Optionally, the cylindrical plug can extend through the bore of the valve seat member. It is also possible for the cylindrical plug to further comprise a plurality of radial protrusions that align the cylindrical plug relative to the cylindrical inner wall of the valve seat member. It is especially preferred that the radial protrusions be sized and spaced to substantially equalize the plug gap around the circumference of the cylindrical plug. These radial protrusions optionally can extend into the bore of the valve seat member.